Positive electrode coating slurry, composite positive plate, preparation method and lithium ion battery

Abstract

The invention discloses positive electrode coating slurry, a composite positive plate, a preparation method and a lithium ion battery. The positive electrode coating slurry comprises a positive electrode material, a sulfide solid electrolyte, a local carbonization binder and an inert organic solvent, and surface groups of the local carbonization binder can be bonded with surface ions of the sulfide solid electrolyte; the positive electrode coating slurry is used for being coated on the surface of a positive electrode current collector to form a positive electrode coating. Surface groups of the local carbonization binder can be bonded with ions on the surface of the sulfide solid electrolyte, the bonding force can greatly improve the cohesiveness, and the bonding effectiveness of the sulfide solid electrolyte is greatly improved; the risks of cracking and peeling of a positive electrode coating and a composite positive plate prepared on the basis of the positive electrode coating slurry can be reduced; and moreover, the inert organic solvent does not generate chemical reaction, so that the lithium ion conduction capability of the positive electrode coating is greatly improved, the acid-base neutralization reaction is also avoided, and the performance of the composite positive electrode plate is favorably improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of secondary batteries, in particular to a positive electrode coating slurry, a composite positive electrode sheet, a preparation method and a lithium ion battery. BACKGROUND

[0002] With the rapid development of the new energy industry, lithium ion batteries are not only applied to mobile phones, notebook computers, small household appliances and the like, but are gradually widely applied to the field of new energy vehicles. In view of the actual needs of consumers for the driving range and driving safety guarantee, high-energy-density and high-safety lithium ion power batteries for new energy vehicles have become the main research and development direction of the current market.

[0003] At present, the lithium ion power battery mainly used is a traditional liquid battery, that is, the transmission of lithium ions between the positive electrode, the separator and the negative electrode is carried out through an electrolyte as a medium. The electrolyte contains highly flammable organic solvents, which increases the safety hazard in the use process of the power battery. A full-solid-state lithium ion battery uses a solid-state electrolyte as a medium for lithium ion conduction between the positive electrode and the negative electrode, completely removes the existence of the electrolyte, guarantees the safety of the battery, and at the same time, due to the extremely low electronic conductivity of the solid-state electrolyte itself, also replaces the existence of the separator, so that the application of a high-nickel and lithium metal system becomes possible, greatly improves the energy density of the lithium ion battery, and effectively alleviates the driving range anxiety of consumers.

[0004] The preparation method of the positive electrode sheet of the traditional liquid lithium ion battery is wet coating, that is, by means of an organic solvent, ingredients are mixed, for example, a binder PVDF (polyvinylidene fluoride) is dissolved in an organic solvent NMP (N-methyl pyrrolidone) to prepare a glue solution, then conductive agents and active substances are gradually added thereto, a slurry with a certain solid content is prepared, the obtained slurry is coated on the surface of a metal current collector by a coating machine, and then heated and dried, so as to obtain a positive electrode sheet.

[0005] However, in the sulfide full-solid-state lithium ion battery system, the use of the electrolyte is completely removed, in order to maintain the necessary lithium ion conduction capacity between the positive electrode materials, a composite mode of the positive electrode material and the sulfide solid-state electrolyte is adopted, the sulfide solid-state electrolyte replaces the electrolyte as a conduction medium to conduct the transmission of lithium ions in the positive electrode sheet, but the sulfide solid-state electrolyte has high reactivity and temperature sensitivity, it is difficult to obtain a positive electrode sheet with the sulfide solid-state electrolyte by means of the traditional wet coating method, which easily leads to a large decrease in the lithium ion conduction capacity of the sulfide solid-state electrolyte, affects the performance of the positive electrode sheet due to acid-base neutralization reaction in the preparation process, and has defects such as easy cracking and peeling. SUMMARY

[0006] To address the problems existing in the prior art, this invention provides a positive electrode coating slurry, a composite positive electrode sheet, a preparation method, and a lithium-ion battery. The technical solution is as follows: This invention provides a positive electrode coating slurry, comprising a positive electrode material, a sulfide solid electrolyte, a locally carbonized binder, and an inert organic solvent, wherein the surface groups of the locally carbonized binder are capable of ionic bonding with the surface of the sulfide solid electrolyte; the positive electrode coating slurry is used to coat the surface of a positive electrode current collector to form a positive electrode coating.

[0007] Furthermore, the degree of local carbonization of the locally carbonized adhesive is 5% to 30%.

[0008] Furthermore, the locally carbonized binder can be reused as a conductive agent for the positive electrode coating.

[0009] Furthermore, the uncarbonized binder in the partially carbonized binder is a carbon chain polymer with a carbon chain as the basic backbone, including at least one of polyethylene, polypropylene, polyvinyl acetate, polyvinyl chloride, polyacrylonitrile, polybutadiene, polyvinyl alcohol formaldehyde, polytetrafluoroethylene, polymethyl methacrylate, natural cellulose, ethyl cellulose, ethyl cellulose modified derivatives, and natural rubber.

[0010] Furthermore, the inert organic solvent is a low-boiling-point inert organic solvent, and the inert organic solvent satisfies at least one of the following characteristics: The boiling point of the inert organic solvent under vacuum is 25℃~80℃; The inert organic solvent includes at least one of n-hexane, dimethylpentane, dichloromethane, dichloroethane, dichlorobutane, isopentane, cyclohexane, cycloheptane, and cyclooctane.

[0011] Furthermore, the mass ratio of the positive electrode coating slurry satisfies at least one of the following characteristics: The mass ratio of the locally carbonized binder to the inert organic solvent is 1:200 to 1:10; The mass ratio of the locally carbonized binder to the sulfide solid electrolyte is 1:50 to 1:2. The mass ratio of the locally carbonized binder to the cathode material is 1:100 to 1:10.

[0012] On the other hand, the present invention also provides a composite positive electrode sheet, comprising a positive current collector and a positive electrode coating located on the surface of the positive current collector, the positive electrode coating being formed on the surface of the positive current collector based on a positive electrode coating slurry as described in any of the preceding claims.

[0013] On the other hand, the present invention also provides a method for preparing a composite positive electrode, comprising: A sulfide solid electrolyte, a locally carbonized binder, an inert organic solvent, and a cathode material are mixed to obtain a cathode coating slurry; the surface groups of the locally carbonized binder can ion-bond with the surface of the sulfide solid electrolyte. The positive electrode coating slurry is coated onto the surface of the positive electrode current collector and then dried to form a positive electrode coating on the surface of the positive electrode current collector, thus obtaining a composite positive electrode sheet.

[0014] Furthermore, the preparation method satisfies at least one of the following characteristics: The locally carbonized adhesive is prepared by heat-treating the adhesive at an inert atmosphere of 100℃ to 300℃ for 2h to 10h. The drying process takes place in a vacuum environment. The vacuum degree of the drying process is less than or equal to a preset vacuum degree, which is -0.02MPa to -0.15MPa. The vacuum resting time for the drying process is less than or equal to a preset time, which is 0.4h to 1.5h.

[0015] On the other hand, the present invention also provides a lithium-ion battery, including the composite positive electrode sheet as described above.

[0016] Implementing this invention has the following beneficial effects: 1. The positive electrode coating slurry of the present invention uses a locally carbonized binder, which can modify the surface bonding chains of the binder. While maintaining its own adhesion, it significantly enhances its dispersion ability in low-boiling-point inert organic solvents, which is beneficial to improving the uniformity of the positive electrode coating slurry. More importantly, the surface groups of this locally carbonized binder can bond with the ionic bonds on the surface of the sulfide solid electrolyte. Compared with traditional binders that provide adhesion through weak van der Waals forces, the bonding force between the two can greatly improve the adhesion and significantly enhance the bonding efficiency of the sulfide solid electrolyte. This helps to reduce the risk of cracking and peeling of the positive electrode coating and composite positive electrode sheet made based on this positive electrode coating slurry. Furthermore, the inert organic solvent will not chemically react with the highly reactive sulfide solid electrolyte, which can greatly improve the lithium-ion conductivity of the positive electrode coating formed based on this positive electrode coating slurry. The inert organic solvent will not become a reaction medium, avoiding the acid-base neutralization reaction between alkaline positive electrode materials, such as high-nickel materials, and acidic sulfide solid electrolytes, which is beneficial to improving the performance of the positive electrode coating and composite positive electrode sheet.

[0017] 2. The locally carbonized binder of the present invention enables binders that do not originally participate in ion transport to participate in ion transport, which greatly improves the electronic conductivity of the positive electrode coating formed based on the positive electrode coating slurry. It can replace the conductive agent and reduce the need for the conductive agent while not affecting the overall electronic conductivity of the positive electrode coating after the positive electrode material and sulfide solid electrolyte are combined, thus saving the raw material cost of the conductive agent in the positive electrode coating and composite positive electrode sheet.

[0018] 3. In the positive electrode coating slurry of the present invention, the local carbonization binder and the inert organic solvent work together to enable the low-boiling-point inert organic solvent to be used in the positive electrode coating slurry. During the process of drying the positive electrode coating slurry to form the positive electrode coating, there is no need for heating and baking. The inert organic solvent can be efficiently removed simply by placing it under a vacuum atmosphere, which reduces the difficulty of preparation, simplifies the preparation process, reduces the production cost, and also prevents the agglomeration and regrowth of sulfide solid electrolyte particles under high temperature conditions, which would lead to a decrease in the lithium-ion conductivity of the positive electrode coating. This is beneficial to improving the performance of the positive electrode coating and the composite positive electrode sheet. Attached Figure Description

[0019] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments will be briefly described below, wherein the same components are represented by the same reference numerals. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0020] Figure 1 This is a physical image of the composite positive electrode sheet prepared according to an embodiment of the present invention; Figure 2 This is a physical image of the positive electrode sheet prepared based on the traditional wet coating system in the comparative example. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments, and therefore should not be construed as limiting the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention can be implemented in orders other than those shown in the figures or descriptions below. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or server that includes a series of steps or units is not necessarily limited to those explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0023] To address at least one of the following problems in existing sulfide-based all-solid-state lithium-ion battery systems, where traditional wet coating methods easily lead to reduced lithium-ion conductivity, acid-base neutralization reactions between raw materials affecting performance, and easy cracking and peeling, this invention provides a positive electrode coating slurry, a composite positive electrode sheet, a preparation method, and a lithium-ion battery. The lithium-ion battery includes the composite positive electrode sheet, and the preparation method for the composite positive electrode sheet is used to prepare the composite positive electrode sheet. The composite positive electrode sheet includes a positive current collector and a positive electrode coating located on the surface of the positive current collector. The positive electrode coating is formed by coating the surface of the positive current collector with a positive electrode coating slurry, that is, the positive electrode coating slurry is used to coat the surface of the positive current collector to form a positive electrode coating.

[0024] Specifically, the positive electrode coating slurry includes a positive electrode material, a sulfide solid electrolyte, a locally carbonized binder, and an inert organic solvent. The locally carbonized binder is obtained by heat-treating the binder to induce localized carbonization on its surface, thus modifying the surface bonding chains of the binder. This allows the surface groups of the locally carbonized binder to ionically bond with the surface of the sulfide solid electrolyte. Compared to traditional binders that rely on weak van der Waals forces for bonding, this locally carbonized binder significantly improves adhesion to the sulfide solid electrolyte through stronger bonding forces, resulting in greatly enhanced adhesion. This allows for maximum coverage of the sulfide solid electrolyte surface. After the positive electrode coating slurry is applied to the surface of the positive electrode current collector to form a positive electrode coating, it effectively prevents the positive electrode coating and composite positive electrode sheet from bonding during subsequent cutting, rolling, and stacking processes. The process of cracking and peeling off the coating significantly improves the acid and alkali resistance of the positive electrode coating, which is beneficial to improving the long-term stability of the composite positive electrode sheet. At the same time, based on this locally carbonized binder, it can work synergistically with inert organic solvents. On the one hand, the inert organic solvents will not chemically react with the highly reactive sulfide solid electrolyte, thereby effectively improving the lithium-ion conductivity of the sulfide solid electrolyte. On the other hand, the inert organic solvents will not act as a liquid medium for the reaction, effectively avoiding the indirect acid-base neutralization reaction between the alkaline positive electrode material and the acidic sulfide solid electrolyte caused by the solvent. This effectively maintains the performance of the positive electrode material and the sulfide solid electrolyte, so that the prepared positive electrode coating and composite positive electrode sheet have excellent lithium-ion conductivity and electronic conductivity, and can exhibit excellent electrochemical performance after being assembled into a lithium-ion battery.

[0025] In some exemplary embodiments, the cathode material is a lithium-ion battery cathode material, including LiNi. x Co y Al （1-x-y） (NCA), LiNi x Co y Mn （1-x-y） The lithium-ion battery cathode material is selected from at least one of (NCM), LiMn2O4 and LiCoO2, wherein x ≥ 0.5 and y ≤ 0.2, and is commercially available.

[0026] In some exemplary embodiments, the sulfide solid electrolyte includes a sulfide solid electrolyte with a silver-germanium sulfide structure; in some preferred embodiments, the sulfide solid electrolyte includes a Li6PS5Cl sulfide solid electrolyte, which is commercially available. This sulfide solid electrolyte has high reactivity but will not react chemically with inert organic solvents, thus not affecting the lithium-ion conductivity and electron conductivity of the sulfide solid electrolyte. Furthermore, the cathode material and the sulfide solid electrolyte are not prone to acid-base neutralization reactions in inert organic solvents, which can effectively prevent adverse effects on the performance of the cathode coating and composite cathode sheet during the preparation process, thereby improving the electrochemical performance of the cathode coating and composite cathode sheet.

[0027] Specifically, the locally carbonized binder can be reused as a conductive agent for the positive electrode coating. This locally carbonized binder is a heat-treated binder with local micro-carbonization characteristics. It can improve adhesion while enabling the binder, which originally did not participate in ion transport, to carry out ion transport, thus significantly improving the electronic conductivity of the locally carbonized binder. It can act as both a binder and a conductive agent. While not affecting the overall electronic conductivity of the positive electrode material and the sulfide solid electrolyte composite, it reduces the need for conductive agents, that is, no additional conductive agents are required, saving raw material costs, further simplifying the preparation process, and also improving the energy density of the composite positive electrode sheet formed by the positive electrode coating slurry of the oil pump.

[0028] Specifically, the uncarbonized binder in the partially carbonized binder is a carbon chain polymer with a carbon chain as its basic backbone, including at least one of polyethylene, polypropylene, polyvinyl acetate, polyvinyl chloride, polyacrylonitrile, polybutadiene, polyvinyl alcohol formaldehyde, polytetrafluoroethylene, polymethyl methacrylate, natural cellulose, ethyl cellulose, ethyl cellulose modified derivatives, and natural rubber, which can be obtained commercially. In some preferred embodiments, the uncarbonized binder in the partially carbonized binder includes at least one of ethyl cellulose and ethyl cellulose modified derivatives. The binder itself has good adhesion and can undergo special heat treatment to achieve partial carbonization. Surface modification allows the surface groups to bond ionicly with the surface of the sulfide solid electrolyte, further improving adhesion through bonding force. It also helps to improve the dispersion ability of the partially carbonized binder in low-boiling-point inert organic solvents, so that the positive electrode coating slurry with the partially carbonized binder forms a glue solution that does not require high-temperature removal. This simplifies the preparation process of the positive electrode coating, composite positive electrode sheet, and lithium-ion battery based on the positive electrode coating slurry, and reduces production costs.

[0029] Specifically, the local carbonization degree of the locally carbonized binder is 5% to 30%; understandably, the local carbonization degree of the locally carbonized binder can be any value within the range of 5% to 30%; for example, the local carbonization degree of the locally carbonized binder can be 5%, 10%, 15%, 17.5%, 20%, 25%, 30%, etc.; within this range of local carbonization degree, not only can the bonding between the contained surface groups and the surface ions of the sulfide solid electrolyte be greatly improved, avoiding cracking and peeling of the positive electrode coating and composite positive electrode sheet in subsequent preparation processes, thus improving the long-term stability of the composite positive electrode sheet, but it can also effectively improve conductivity and save costs. This method saves on the cost of conductive agent raw materials while increasing the energy density of the composite cathode sheet. Furthermore, it enhances the cathode's dispersion ability in low-boiling-point inert organic solvents, facilitating the formation of a gel system—the cathode coating slurry—that does not require high-temperature removal. This simplifies the preparation process of the cathode coating based on the slurry, reduces costs, and avoids the regrowth of sulfide solid electrolyte particles caused by heat during traditional high-temperature drying, which could affect lithium-ion conductivity. This significantly improves the preparation efficiency and yield of the cathode coating slurry preparation method, enhancing the electrochemical performance of the cathode coating, composite cathode sheet, and lithium-ion battery.

[0030] Specifically, the inert organic solvent is a low-boiling-point inert organic solvent with a boiling point of 25°C to 80°C under vacuum. Understandably, the boiling point of the inert organic solvent under vacuum can be any value within the range of 25°C to 80°C. For example, the boiling point of the inert organic solvent under vacuum can be 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc. Within this boiling point range, the boiling point of the inert organic solvent under vacuum is relatively low. During the subsequent coating of the positive electrode slurry onto the surface of the positive electrode current collector and drying to form the positive electrode coating, no heating or baking is required. Simply placing it in a vacuum environment allows the inert organic solvent to be removed in a very short time. This avoids the agglomeration and particle regrowth of the sulfide solid electrolyte during baking, which would affect the lithium-ion conductivity of the composite positive electrode sheet. This is beneficial for improving the electrochemical performance of the positive electrode coating and the composite positive electrode sheet.

[0031] Specifically, the inert organic solvent includes at least one of n-hexane, dimethylpentane, dichloromethane, dichloroethane, dichlorobutane, isopentane, cyclohexane, cycloheptane, and cyclooctane, which can be obtained commercially. On the one hand, the inert organic solvent has extremely high inertness, which means it will not react with the sulfide solid electrolyte and reduce its lithium-ion conductivity, nor will it act as a reaction medium between the alkaline cathode material and the acidic sulfide solid electrolyte to undergo acid-base neutralization reaction, thus greatly improving the performance of the cathode coating and composite cathode sheet. On the other hand, the inert organic solvent has a low boiling point under vacuum, and can be removed by vacuum placement without high-temperature heating, which simplifies the preparation of the cathode coating and composite cathode sheet and is also conducive to improving the lithium-ion conductivity of the solid electrolyte in the cathode sheet.

[0032] Specifically, the mass ratio of the locally carbonized adhesive to the inert organic solvent is 1:200 to 1:10; it can be understood that the mass ratio of the locally carbonized adhesive to the inert organic solvent can be any value within the range of 1:200 to 1:10; for example, the mass ratio of the locally carbonized adhesive to the inert organic solvent can be 1:200, 1:150, 1:100, 1:90, 1:75, 1:60, 1:50, 1:20, 1:10, etc.

[0033] Specifically, the mass ratio of the locally carbonized binder to the sulfide solid electrolyte is 1:50 to 1:2; it can be understood that the mass ratio of the locally carbonized binder to the sulfide solid electrolyte can be any value from 1:50 to 1:2; for example, the mass ratio of the locally carbonized binder to the sulfide solid electrolyte can be 1:50, 1:25, 1:20, 1:10, 1:7.5, 1:5, 1:3, 1:2, etc.

[0034] Specifically, the mass ratio of the local carbonized binder to the positive electrode material is 1:100 to 1:10; understandably, the mass ratio of the local carbonized binder to the positive electrode material can be any value from 1:100 to 1:10; for example, the mass ratio of the local carbonized binder to the positive electrode material can be 1:100, 1:75, 1:50, 1:25, 1:20, 1:10, etc.

[0035] Thus, within the mass ratio range of the local carbonized binder, cathode material, sulfide solid electrolyte, and inert organic solvent, the cathode coating slurry exhibits excellent adhesion, effectively preventing the cathode coating formed based on the slurry from cracking and peeling during subsequent preparation. It also improves the conductivity and energy density of the cathode coating and composite cathode sheet, and enables the cathode coating slurry to form a glue system that does not require high-temperature removal, simplifying the preparation process, reducing production costs, and improving preparation efficiency and yield.

[0036] On the other hand, the present invention provides a composite positive electrode sheet, comprising a positive current collector and a positive electrode coating located on the surface of the positive current collector, wherein the positive electrode coating is formed by coating the surface of the positive current collector with the positive electrode coating slurry as described above.

[0037] On the other hand, the present invention provides a method for preparing a composite positive electrode, comprising: A sulfide solid electrolyte, a locally carbonized binder, an inert organic solvent, and a cathode material are mixed to obtain a cathode coating slurry; the surface groups of the locally carbonized binder can ion-bond with the surface of the sulfide solid electrolyte. The positive electrode coating slurry is coated onto the surface of the positive electrode current collector and then dried to form a positive electrode coating on the surface of the positive electrode current collector, thus obtaining a composite positive electrode sheet.

[0038] Specifically, the positive electrode coating slurry obtained by mixing sulfide solid electrolyte, local carbonization binder, inert organic solvent and positive electrode material can include: A local carbonized adhesive and an inert organic solvent are mixed and stirred to obtain an adhesive solution; In an inert gas protective atmosphere, the sulfide solid electrolyte is mixed with the adhesive solution and stirred to obtain the initial slurry; The cathode material is mixed and stirred with the initial slurry to obtain the cathode coating slurry.

[0039] Next, the positive electrode current collector includes at least one of aluminum foil and carbon-coated aluminum foil. A positive electrode coating slurry is coated on the surface of the positive electrode current collector. The drying process can quickly remove the inert organic solvent and form a positive electrode coating to obtain a composite positive electrode sheet. Then, the composite positive electrode sheet is cut to obtain a composite positive electrode sheet of the target shape. The composite positive electrode sheet of the target shape is then rolled to obtain a dense sulfide solid point mechanism composite positive electrode sheet.

[0040] Furthermore, in embodiments of the present invention, the equipment used for stirring includes equipment such as a magnetic stirrer that can perform stirring; the equipment used for coating the positive electrode coating slurry includes equipment such as a flat plate coater that can perform coating; the equipment used for cutting includes equipment such as a cutting machine that can perform cutting; and the equipment used for rolling includes equipment such as a vertical double roller machine that can perform rolling. The present invention does not specifically limit these.

[0041] Specifically, the locally carbonized adhesive is prepared by heat-treating the adhesive at an inert atmosphere of 100°C to 300°C for 2 to 10 hours; the inert atmosphere includes at least one of nitrogen and argon atmospheres; understandably, the temperature of the heat treatment can be any value from 100°C to 300°C, and the time can be any value from 2 hours to 10 hours; for example, the temperature of the heat treatment can be 100°C, 120°C, 150°C, 175°C, 200°C, 250°C, 300°C, etc., and the time can be 2 hours, 4 hours, 5 hours, 7 hours, 9 hours, 10 hours, etc.; in this way, the degree of local carbonization of the adhesive can be precisely controlled, which improves the adhesion, the conductivity of the locally carbonized adhesive, and its dispersion ability in low-boiling-point inert organic solvents, making it easier to form a glue system that does not require high-temperature removal when combined with low-boiling-point inert organic solvents.

[0042] Specifically, during the drying process of the positive electrode coating slurry coated on the surface of the positive electrode current collector, the drying environment is a vacuum environment, which eliminates the need for high-temperature drying. This avoids the regrowth of sulfide solid electrolyte particles due to heat, which would affect the lithium-ion conductivity of the positive electrode coating. Furthermore, the low-boiling-point inert organic solvent can be effectively removed directly in a vacuum atmosphere, simplifying the preparation process of the positive electrode coating and reducing the difficulty and cost of preparation.

[0043] Specifically, the vacuum degree of the drying process is less than or equal to a preset vacuum degree, which is -0.02MPa to -0.15MPa. Understandably, the preset vacuum degree can be any value within the range of -0.02MPa to -0.15MPa. For example, the preset vacuum degree can be -0.02MPa, -0.05MPa, -0.10MPa, -0.12MPa, -0.15MPa, etc. For instance, in some specific embodiments, the preset vacuum degree can be -0.08MPa, meaning the vacuum degree of the drying process is less than or equal to -0.08MPa. In some preferred embodiments, the preset vacuum degree can be -0.05MPa, meaning the vacuum degree of the drying process is less than or equal to -0.05MPa.

[0044] Specifically, the vacuum resting time for the drying process is less than or equal to a preset time, which is 0.4h to 1.5h. Understandably, the preset time can be any value within the range of 0.4h to 1.5h. For example, the preset time can be 0.4h, 0.5h, 0.8h, 1h, 1.5h, etc. For instance, in some specific embodiments, the preset time can be 1h, that is, the vacuum resting time for the drying process is less than or equal to 1h. In some preferred embodiments, the preset time can be 0.5h, that is, the vacuum resting time for the drying process is less than or equal to 0.5h.

[0045] Thus, under this vacuum level and after the aforementioned vacuum resting time, inert organic solvents can be effectively removed, avoiding high-temperature conditions and the potential reduction in lithium-ion conductivity of sulfide solid electrolytes caused by high-temperature conditions. This is beneficial for improving the preparation efficiency and yield of composite cathode sheets, and enhancing their performance.

[0046] On the other hand, the present invention provides a lithium-ion battery including the composite positive electrode sheet as described above; in some exemplary embodiments, the lithium-ion battery includes a sulfide all-solid-state lithium-ion battery, wherein the composite positive electrode sheet is not easy to crack and peel off, which is also beneficial to improving the long-term stability of the lithium-ion battery.

[0047] The following describes specific embodiments of the present invention in conjunction with the above-mentioned positive electrode coating slurry, composite positive electrode sheet, preparation method, and lithium-ion battery.

[0048] Example 1 The lithium-ion battery in this embodiment is prepared through the following steps: 1. Mix cellulose, a locally carbonized adhesive with a local carbonization degree of 30%, and isopentane, an inert organic solvent, at a mass ratio of 3:100, and stir to obtain an adhesive solution.

[0049] In an inert gas protective atmosphere, the sulfide solid electrolyte Li6PS5Cl, the positive electrode material and the adhesive solution are mixed and stirred according to a mass ratio of 1:5:14 for the local carbonized binder, the sulfide solid electrolyte and the positive electrode material to obtain the positive electrode coating slurry.

[0050] A positive electrode coating slurry is coated onto the surface of a carbon-coated aluminum foil current collector and dried at room temperature under -0.08 MPa for 1 hour to form a positive electrode coating on the surface of the current collector, thus obtaining a composite positive electrode sheet, which is then cut and rolled.

[0051] The negative electrode is a lithium metal negative electrode, and the electrolyte layer is a sulfide solid electrolyte. The composite positive electrode, lithium metal negative electrode and electrolyte layer are assembled into a sulfide all-solid-state battery.

[0052] Example 2 The difference between this embodiment and Embodiment 1 is that the degree of local carbonization of cellulose is 10%; the rest is the same as in Embodiment 1.

[0053] Example 3 The difference between this embodiment and Embodiment 1 is that the drying process is carried out by placing the sample at room temperature under a pressure of -0.05 MPa for 5 hours; otherwise, it is the same as Embodiment 1.

[0054] Example 4 The difference between this embodiment and Embodiment 1 is that the vacuum resting time for the drying process is 0.5 hours; the rest is the same as in Embodiment 1.

[0055] Example 5 The difference between this embodiment and Example 1 is that the inert organic solvent is dichloromethane; otherwise, it is the same as Example 1.

[0056] Example 6 The difference between this embodiment and Example 1 is that the inert organic solvent is cycloheptane; otherwise, it is the same as Example 1.

[0057] Comparative Example 1 The difference between this comparative example and Example 1 is that ordinary cellulose without heat treatment is used as the binder; otherwise, it is the same as Example 1.

[0058] Comparative Example 2 The difference between this comparative example and Example 1 is that untreated ordinary cellulose is used as a binder, and a conductive agent is added. The mass ratio of binder, sulfide solid electrolyte, conductive agent and positive electrode material is 3:25:2:70; the rest is the same as Example 1.

[0059] Comparative Example 3 The difference between this comparative example and Example 1 is that the inert organic solvent is dodecane with a high boiling point, and the drying process is carried out under a vacuum of -0.08 MPa and baking at 120°C for 2 hours; the rest is the same as Example 1.

[0060] Comparative Example 4 The difference between this comparative example and Example 1 is that the binder is PVDF, the organic solvent is NMP, and 2% conductive agent is added; otherwise, it is the same as Example 1.

[0061] Comparative Example 5 The difference between this comparative example and Example 1 is that the binder is PVDF, the inert organic solvent is isopentane, and 2% conductive agent is added; the rest is the same as Example 1.

[0062] The performance of the sulfide all-solid-state batteries of Examples 1-6 and Comparative Examples 1-5 was tested. The discharge specific capacity at 0.1C rate at room temperature and the capacity retention rate after 50 cycles at 0.5C rate were tested respectively. The test results are shown in Table 1 below.

[0063] Table 1 Performance test results of the examples and comparative examples

[0064] First, such as Figure 1 and Figure 2As shown, compared with the positive electrode sheet prepared by the traditional wet coating system, the composite positive electrode sheet prepared in this application has a better morphology and superior performance. As shown in Table 1, compared with the uncarbonized ordinary cellulose binder in Comparative Example 1 and the traditional binder in Comparative Examples 4-5, the lithium-ion batteries in Examples 1-6 use a partially carbonized binder and a low-boiling-point inert organic solvent, which effectively improves the discharge specific capacity and cycle stability. Furthermore, compared with the scheme in Comparative Example 2 that requires the addition of a conductive agent, the embodiments of this application can prepare lithium-ion batteries with similar electrochemical performance without the need for additional conductive agents, effectively simplifying the preparation process and saving raw material costs. In addition, compared with the scheme in Comparative Example 3 that uses a high-boiling-point organic solvent, the method of efficiently removing the inert organic solvent without high-temperature drying in the embodiments of this application can effectively prevent the sulfide solid electrolyte from undergoing particle regrowth due to heating, which would affect lithium-ion conduction and greatly improve the performance of the lithium-ion battery.

[0065] The above description is merely some embodiments of the present invention and is not intended to limit the present invention. Those skilled in the art should understand that the present invention can have various changes and modifications, and any modifications, equivalent substitutions and improvements made in accordance with the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A positive electrode coating slurry, characterized by, The positive electrode coating slurry comprises a positive electrode material, a sulfide solid electrolyte, a partially carbonized binder, and an inert organic solvent, wherein surface groups of the partially carbonized binder can be ionically bonded to the surface of the sulfide solid electrolyte; and the positive electrode coating slurry is used to coat the surface of a positive electrode current collector to form a positive electrode coating.

2. The positive electrode coating slurry according to claim 1, characterized by, The partially carbonized binder has a carbonization degree of 5% to 30%.

3. The positive electrode coating slurry according to claim 1, wherein The partially carbonized binder can be reused as a conductive agent of the positive electrode coating.

4. The positive electrode coating slurry according to claim 1, wherein The uncarbonized binder in the partially carbonized binder is a carbon chain polymer with a carbon chain as a basic skeleton, and includes at least one of polyethylene, polypropylene, polyvinyl acetate, polyvinyl chloride, polyacrylonitrile, polybutadiene, polyvinyl formal, polytetrafluoroethylene, polymethyl methacrylate, natural cellulose, ethyl cellulose, ethyl cellulose modified derivatives, and natural rubber.

5. The positive electrode coating slurry according to any one of claims 1 to 4, characterized by, The inert organic solvent is a low-boiling inert organic solvent, and the inert organic solvent satisfies at least one of the following characteristics: The boiling point of the inert organic solvent in a vacuum environment is 25°C to 80°C. The inert organic solvent includes at least one of n-hexane, dimethylpentane, dichloromethane, dichloroethane, dichlorobutane, isopentane, cyclohexane, cycloheptane, and cyclooctane.

6. The positive electrode coating slurry according to any one of claims 1 to 4, characterized by, The mass ratio of the positive electrode coating slurry satisfies at least one of the following characteristics: The mass ratio of the partially carbonized binder to the inert organic solvent is 1:200 to 1:10; The mass ratio of the partially carbonized binder to the sulfide solid electrolyte is 1:50 to 1:2; The mass ratio of the partially carbonized binder to the positive electrode material is 1:100 to 1:

10.

7. A composite positive electrode sheet, characterized by The positive electrode coating slurry comprises a positive electrode material, a sulfide solid electrolyte, a partially carbonized binder, and an inert organic solvent, wherein surface groups of the partially carbonized binder can be ionically bonded to the surface of the sulfide solid electrolyte; and the positive electrode coating slurry is used to coat the surface of a positive electrode current collector to form a positive electrode coating.

8. A method for producing a composite positive electrode sheet, characterized by The preparation method comprises the following steps: The sulfide solid electrolyte, the partially carbonized binder, the inert organic solvent, and the positive electrode material are mixed to obtain a positive electrode coating slurry; surface groups of the partially carbonized binder can be ionically bonded to the surface of the sulfide solid electrolyte; The positive electrode coating slurry is coated on the surface of a positive electrode current collector and subjected to a drying treatment to form a positive electrode coating on the surface of the positive electrode current collector, thereby obtaining a composite positive electrode sheet.

9. The method of claim 8, wherein the method is characterized by, The preparation method satisfies at least one of the following characteristics: The partially carbonized binder is prepared by heat treating the binder in an inert atmosphere at 100°C to 300°C for 2h to 10h; The drying treatment is performed in a vacuum environment; The vacuum degree of the drying treatment is less than or equal to a preset vacuum degree, and the preset vacuum degree is -0.02MPa to -0.15MPa; The vacuum standing time of the drying treatment is less than or equal to a preset time, and the preset time is 0.4h to 1.5h.

10. A lithium-ion battery, characterized by, The composite positive electrode sheet according to claim 7.

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